The monomaleate salt of 1-((2R,4R)-2-(1H-benzo[d]imidazol-2-yl)-1-methylpiperidin-4-yl)-3-(4-cyanophenyl)urea has the structure of Formula (I):

The compound 1-((2R,4R)-2-(1H-benzo[d]imidazol-2-yl)-1-methylpiperidin-4-yl)-3-(4-cyanophenyl)urea (PF-04449913) has been assigned the International Nonproprietary Name (INN) glasdegib, as described in WHO Drug Information, Vol. 29, No. 1, page 89 (2015), referencing the alternative chemical name N-[(2R,4R)-2-(1H-benzoimidazol-2-yl)-1-methylpiperidin-4-yl]-N′-(4-cyanophenyl)urea. The maleate salt of Formula (I) may also be referred to herein as 1-((2R,4R)-2-(1H-benzo[d]imidazol-2-yl)-1-methylpiperidin-4-yl)-3-(4-cyanophenyl)urea maleate or glasdegib maleate.
Preparation of glasdegib as a hydrochloride salt is described in International Patent Application No. PCT/IB2008/001575, published as WO 2009/004427, and in U.S. Pat. Nos. 8,148,401 and 8,431,597, the contents of each of which are incorporated herein by reference in their entirety.
Glasdegib is an inhibitor of the smoothened receptor (Smo), a component of the hedgehog (Hh) signaling pathway that is a potential therapeutic target in a number of human cancers, in particular hematologic malignancies including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myelomonocytic leukemia (CMML), myelofibrosis (MF) and myelodysplastic syndromes (MDS). The discovery of glasdegib and its preparation as a dihydrochloride monohydrate salt has been described by Munchhof et al. (Med. Chem., Lett, 2012, 3:106-111). A process for the asymmetric synthesis of glasdegib has been described by Peng et al. (Org. Lett., 2014, 16:860-863).
The present invention provides crystalline glasdegib maleate having improved properties, such as improved chemical and thermal stability upon storage, and decreased hygroscopicity, while maintaining chemical and enantiomeric stability.
The invention also provides a crystalline glasdegib imidazole complex (1:1) and a crystalline glasdegib (S)-mandelate salt, which are useful for the preparation of glasdegib maleate and other salts in high yield and with high chemical purity.